Speedometer error?

Both of my 525t's have/ had speedo error of 9% fast. (Reads fast- Spedo says 70MPH, real speed is 64).
The factory claimed that 9% was acceptable and within factory specs. I say/ said bullsh... Both cars had/ have factory tires & wheels. In Germany, I was told that TUV regulations spelled out an error no greater than 3% across the middle 1/3rd of the gauge.
I would think there would be an adjustable rheostat or something to dial it in. Has anyone else noticed this kind of error? Granted, it does help with the tendency to speed.
And, what if you had a warranty problem when your odometer read 50,001?

Thats strange- I checked my actual speed over about 50 miles of mile markers by my watch (time). I have done this 2 or 3 times on long drives up Hwy.395. Both the spedo and odometer were off 9 - 10%. Stuts

My E36 speedometer also reads higher than the actual speed-( could be a blessing at times ) I noticed this when I first got the car in 2000 and the dealer checked the car and said it was within 10% which is an acceptable tolerance. I have 2 other cheaper cars and they are very accurate. Don't understand why a company that has a reputation for quality and precision can't get this simple thing right.

I've experienced the same thing with BMW instrument inaccuracy in general. The first question is, what represents an accurate measure? Earlier in this thread, someone used mile marker posts on a highway. Are they placed accurately? Obviously the longer the test (e.g., 100 miles vs. 1 mile) the greater the accuracy because it reduces the impact of human error (both placing the posts and detecting arrival at a given point.)

I've used my GPS as a measure against both the speedometer and odometer. I'm making a presumption the GPS is highly accurate, but don't know that to be a fact.

Assuming it is, my experience shows that an indicated 70 mph on the speedometer is 66 mph by GPS, which is about a 6% error. Ironically, my two other cars (a Saturn and Dodge Caravan) have speedometers that are highly accurate relative to the GPS. In both cars, 70 is 70 mph. Go figure, since both cars together cost less than half the purchase price of my BMW (although speedometer accuracy was not remotely the determining factor in my selection.)

The odometer error relative to the GPS was (as I recall) only about 3% overstated, this done over a long trip comparing the trip odometer with the miles traveled recorded on the GPS. Interestingly, comparing the onboard computer calculation of MPG versus actual fuel consumption (over a number of consecutive fill-ups at the same fuel pump to reduce that error) showed about the same error rate resulting in an overstating of MPG by the onboard computer. I presume the computer gets the same measure of distance travelled as the odometer.

Also, I've read in a number of places that the coolant temperature gauge is "buffered", displaying a constant position on the gauge even though the coolant itself is varying in temperature. Only when the temperature exceeds a certain amount will it move above the "normal" position, making it a glorified idiot light. Personally, I would prefer an accurate rendition of actual coolant temperature. Why? Well, I had a Volvo that when it got older, I noticed the coolant temperature would creep up at highway speeds (i.e., under load.) This helped me diagnose a partially clogged radiator before it became a problem. I don't believe the BMW gauge would be as helpful.

Also, I've read in a number of places that the coolant temperature gauge is "buffered", displaying a constant position on the gauge even though the coolant itself is varying in temperature. Only when the temperature exceeds a certain amount will it move above the "normal" position, making it a glorified idiot light. Personally, I would prefer an accurate rendition of actual coolant temperature. Why? Well, I had a Volvo that when it got older, I noticed the coolant temperature would creep up at highway speeds (i.e., under load.) This helped me diagnose a partially clogged radiator before it became a problem. I don't believe the BMW gauge would be as helpful.

Then people would bring in their car when at idle their water temp went up slightly and lowered when accelerating. I guess it was easier to dummy down the gauge. Personally I like my E30 water temp gauge. It actually works. My E36 stays at 12:00 o'clock whether I'm at idle or WOT down the front straight at VIR.

Back to the GPS to stay on topic, I think the GPS is more accurate in a straight line.
When I used it to check rallies, I found once I got into a twisty area, the mileage was no longer accurate.

Yes, and I did my testing tooling along relatively straight Interstate highways. I agree with your comment ... GPS accuracy for this purpose probably does degrade in the twisties. Mostly speculation since I don't have proof either way.

While they were at it, why didn't BMW give us other gauges/displays? I'd like to know about system voltage, oil temp, etc.

My theory on MPG is, MPG is inversely proportional to the amount of fun you have.

Couldn't be truer. It is also inversely proportional to the size of the headache you have.

The GPS isn't accurate enough regardless of the situation. Most regular auto GPS's are accurate to within a few meters, but a few meters is quite a distance. It also depends on how many that "few" meters actually is. Sometimes 10, perhaps. But, GPS is not a reliable way to measure speed anyway because it's not entirely in real time. It takes a fraction of a second or sometimes a second to update your speed on the screen when it changes. That's not accurate at all. Of course I say this about your run-of-the-mill Circuit City GPS. There may be more complicated and more expensive specialized GPS's that may be accurate, but I don't know about any of those.

Isn't there some kind of OBDII tool that shows you mpg, revs/min., and speed in real time?

Thats strange- I checked my actual speed over about 50 miles of mile markers by my watch (time). I have done this 2 or 3 times on long drives up Hwy.395. Both the spedo and odometer were off 9 - 10%. Stuts

Mine is off by about 7% (reads too high) on both the speedometer and odometer. I've checked is with mile markers and 3 GPS units. My Volvo, Lexus, and Toyota Rav are all spot on. The Volvo agrees with my GPS to the tenth of a mile -- even after several hundred miles.

My new 2009 128i speedometer shows 70 when both my GPS show 65. I called the dealer and customer relations and they both told me that they are setup to a -0 +10% error so we dont get a ticket. I told them that this was a bunch of *(&^%&^&^&^ and that they should calibrate it on the money. My Ford F150 is only off 1mph, not 5. Only if it is more than 10% will they recalibrate it. Since it's all electronics/software, I'm sure someone, somewhere nows how to calibrate this so it's right on the money.

Here's a link to the info on how to unlock your OBC for the e39. You'll find the data you desire hidden away behind a few simple presses of your reset buttons and VOILA, the secret world of technicians is revealed!

EDIT: BTW, afaik the built-in OD and speedo errors are programmed in at the factory for a specific reason. I can't remember the exact reason but I definitely read about it on another forum (perhaps BF.c). I've just resigned myself to the fact and drive 5-mph over the shown speed with the knowledge that 85 is actually 80...easy fix. LOL